1. Field of the Invention
The invention relates to a process for composting decaying material or organic waste and/or sewage sludge.
2. Description of the Prior Art
German Auslegeschrift No. 24 32 744 discloses a treatment for sewage sludge wherein the sludge, after the addition of carbon carriers, may be mixed and aerated in a pre-composting silo. After a dwell time of 24 hours, it is conveyed to the top stage of a multi-stage composting silo in order to aerate the decaying material for a time period between 12 and 14 hours with air which has been preheated to +26.degree. C. The decaying material, so treated, is then transferred to a second stage of the silo and aerated once again there with air preheated to +26.degree. C. This process is repeated in a third, fourth and fifth stage of the silo. Thereafter, 80% of the decaying material, with the addition of 25 kg of calcium cyanamide per cubic meter of decaying material, is conveyed via the pre-composting silo to a post-composting silo or an aeration container for a 8 to 10 day post-aeration with fresh air. The remaining 20% of the decaying material is brought together and mixed in the pre-composting silo with freshly supplied sewage sludge and a once again predetermined amount of a carbon carrier.
The sewage sludge is to be decayed, hygienized and post-matured completely in this manner in several consecutive processing steps, so that the final product is agriculturally completely usable. Since the treatment time in the individual is 24 hours in each case, a continuous throughput should be possible.
Experience has shown that gravity feed and compressed air conveying of sewage sludge, converted into a decayable state, is not possible. It is thus necessary to assign to each stage of such a multistage process mechanical conveying means, such as, for example, screw conveyors, by means of which the decaying material is constantly turned over. The constant mechanical intervention, however, prevents the build-up of an effective biological mass within the decaying material and destroys the mycelar hyphae so that, in spite of the large expenditure for equipment, complete decaying of the material becomes impossible. Moreover, the proposed interval aeration of the silo in which the decaying takes place, in conjunction with a stirrer, is a hindrance for good initiation of the decaying. As a result of the interval aeration, suitable living conditions for multiplication are offered to only a few strains of bacteria and microorganisms, which normally take part in the decaying process. Also, because of the proposed manner of guiding the air, this can not be changed in the subsequent stages of the decaying. Finally, the different aeration of each stage of the decaying requires a high expenditure for equipment which is complicated to use.
In order to obtain a hygienically unobjectionable, biologically active, valuable humus material as end product of a decaying process which is to be carried out on a large, industrial scale, insofar as possible, optimal living conditions should be offered to all microorganisms and bacteria present in the decaying material. This allows them to multiply rapidly and through their metabolic processes, carry out the decay and conversion of the organic waste in the humus within a shorter time than is required in nature.
Such a decaying process is described, for example, in German Auslegeschrift No. 22 53 009. In this process, by carefully keeping to the parameters which influence the decaying process and which are controlled essentially by the supply of air, a differential layering of heat and oxygen and, consequently, a differential distribution of specific bacteria, is achieved within the column of material within an aeration reactor. This leads to a differentiated activity of aerobic and anaerobic bacteria, which is optimal for the decaying process.
In such a decaying process, the decaying material passes through the aeration reactor within a period of about 14 to 20 days, the dwell time being determined essentially by the desired degree of maturity of the compost obtained as the final product. If the decaying time is too short, an immature compost is obtained, which then must be matured preferably in compost heaps. Such a maturing process requires special areas and, due to atmospheric effects, is completely uncontrolled. It also happens that, in efforts to increase profits, compost which is not yet mature comes on the market since the external, visible layers of the composte piles already have the appearance and odor of fresh forest soil. Finally, valuable nitrogen is lost during the maturing processing a compost pile.